1. Field of the Invention
The present invention relates to a semiconductor device, in particular, an isolating oxide film in a semiconductor integrated circuit device and a pattern of an electrical active region surrounded by the isolating oxide film.
2. Discussion of Background
In recent years, in accordance with micro miniaturization and high-integration of elements of semiconductor integrated circuit devices, design rules become further specific, and a process becomes very complicated. Especially, in an element isolation, a trench-type isolating oxide film, suitable for micro miniaturization, is widely used. Therefore, it is very important to properly embed the isolating oxide film in a trench without spoiling a performance of an electrical active device region and to polish by a CMP method with high reliability.
FIG. 9 is a plan view of a conventional semiconductor device in which elements are isolated. As illustrated in FIG. 9, a pattern 1 of an electrical active device region, in which elements are formed, is arranged so as to be surrounded by an isolating region 2. Particularly, numerical reference 1a designates a micro width pattern in the electrical active device region, hereinbelow the micro width pattern is referred to as an actual micro pattern 1a. 
FIGS. 10a and 10b are cross-sectional views of the conventional semiconductor device illustrated in FIG. 9, in which semiconductor device the elements are isolated. FIG. 10a is the cross-sectional view taken along a line A9—A9 in FIG. 9, in which the isolating region 2, being relatively wide, is shown. FIG. 10b is the cross-sectional view taken along a line B9—B9 in FIG. 9, wherein the actual micro pattern 1a, which is surrounded by the isolating regions 2 on both of sides, is shown.
An element isolation in a semiconductor device is formed by sequentially arranging an underlayer oxide film 4 and a nitride film 5 on a semiconductor substrate 3. Thereafter, after selectively etching to remove a part of the nitride film 5, to be the isolating region 2, the semiconductor substrate 3 is etched using a mask of the nitride film 5, whereby a trench having a predetermined depth is formed. Succeedingly, after forming an isolating oxide film 7 on an entire surface of the semiconductor substrate 3 so as to fill an inside of the trench 6, the isolating oxide film 7 is abraded by a CMP method to remove the isolating oxide film 7 on the nitride film 5 and leave the isolating oxide film 7 only inside the trench 6, whereby a trench-type isolating oxide film 7a is formed. The nitride film 5 and the underlayer oxide film 4 are removed after forming the element isolation.
However, the conventional semiconductor device has a problem that an abrading rate is decreased at around a region where the nitride film 5 is formed by an influence of the nitride film 5 because the isolating oxide film 7 on the nitride film 5 is removed by abrasion using a CMP method, the abrading rate of the nitride film 5 is low. On the contrary, in the wide isolating region 2, i.e. the trench-type isolating oxide film 7a, illustrated in FIG. 10a, the abrading rate is high, and a sink is produced in a film in its thickness direction by dishing especially in a central portion. Therefore, there are problems that a flatness of a surface is deteriorated, and a later process of patterning using a lithography technique is inappropriately patterned.
Further, as illustrated in FIG. 10b, when the actual micro pattern 1a is surrounded by the wide isolating regions 2, i.e. the trench-type isolating oxide films 7a, there is a case that a part or all of the nitride film 5 of the actual micro pattern 1a is abraded by overpolishing as illustrated in FIG. 11 because an abrading rate for the trench-type isolating oxide films 7a is high. Therefore, there are problems that the film thicknesses of the trench-type isolating oxide films 7a have further large sinks, and electrical characteristics of element are deteriorated such that a threshold value is deteriorated by an inverse narrow channel effect in properties of transistor and a leakage current is increased.
In order to improve the above-mentioned problems, in a conventional technique, a dummy pattern, being an active region of a dummy, is located in the isolating region 2 to improve uniformity of an abrading rate by a CMP method.
FIGS. 12 and 13 are plan views illustrating examples of improvement of conventional semiconductor devices, in which dummy patterns 8, i.e. active regions of a dummy, are arranged in the isolating region 2 of the semiconductor device illustrated in FIG. 9. In FIG. 12, relatively small dummy patterns 8a are bedded in the isolating region 2. In FIG. 13, relatively large dummy patterns 8b are bedded in the isolating region 2.
When the isolating oxide film 7 is abraded by the CMP method in a case illustrated in FIG. 12, an abrading rate for a region, where the small dummy patterns 8a cluster, is lowered. Accordingly, there is a case that the isolating oxide film 7 is left on the nitride film 5 of the dummy pattern 8a by under-polishing as illustrated in a cross-sectional view of FIG. 14. In this case, not only the isolating oxide film 7 but also the nitride film 5 and an underlayer oxide film 4, which are located on a lower side of the isolating oxide film 7, are not removed by a succeeding removing step, whereby flatness of a surface is extremely spoiled, and it becomes difficult to pattern in a later step.
Further, in the case illustrated in FIG. 13, because the dummy patterns 8b are large, there are areas where the dummy patterns are not arranged in a periphery of the actual pattern 1. Especially, when the dummy patterns 8b do not exist in the periphery of the actual micro pattern 1a, a cross-sectional view taken along a line B13—B13 is similar to that in FIG. 10b. As illustrated in FIG. 11, because of the high abrading rate or the trench-type isolating oxide films 7a, there is a case that a part or all of the nitride film 5 of the actual micro pattern 1a is abraded by over-polishing. Therefore, as described above, the sinks in the trench-type isolating oxide films 7a become further large, whereby electrical characteristics of element are deteriorated.